Powderable reactive resin compositions

ABSTRACT

1. A reactive resin composition, which is a fusible, solid optionally foamable, heat curable, epoxy functional reaction prouct with a Kofler Heat Bank melting point of not less than 55° C., formed by mixing together 
     (A) epoxy resins of epoxy group containing compounds 
     (B) an amine solidifying system present in insufficient quantities to cause gelation after all the amino hydrogen atoms are consumed by epoxy groups, under the reaction conditions chosen for (A) and (B), and which yields a product with a Kofler Heat Bank melting point of greater than 55° C. and less than 120° C. and melting point stability of at least six months normal workshop temperatures, 
     (C) a hardener system for (A) and the reaction product of (A) and (B) which is different from (B) and remains substantially unreacted under the conditions of reaction chosen for (A) and (B) with (A) and (B) and which is of low reactivity at normal workshop temperatures in the final solid epoxy formulation, optionally, 
     (D) an expanding agent which is of low reactivity under the conditions of reaction chosen for (A) and (B) and which is of low reactivity at normal workshop temperatures in the final solid epoxy formulation, and optionally 
     (E) other additives that may be required to modify the physical properties of the cured or uncured composition.

This invention relates to heat curable, solid epoxy resin compositionswhich are especially suitable for use in powder form but are also usefulin other configurations such as pellets, tablets, rods and sticks forexample and in general have a Kofler Heat Bank melting point greaterthan 55° C. The compositions can also be foamable.

Solid, curable epoxy resin compositions are well known and find manyuseful commercial applications. These include for instance, protectiveand decorative coatings, electrical insulation, encapsulants, mouldingcompounds, adhesives and matrix resins for fibre reinforced composites.

Solid heat curable epoxy resin compositions are eventually used by a hotmelt process whether it is by application in the already molten state orapplied to an already heated surface and melts on contact or applied bytechniques such as electrostatic spraying or placing in a mould and thenmelted and cured on heating.

For solid epoxy resin compositions to be useful in powder form they needto have a melting point as determined by the Kofler Heat Bank method ofat least 55° C. and preferably 65° C. Powders with lower melting pointsrapidly sinter together when stored at normal workshop temperatures(15°-30° C.) and become unpourable. Low melting powders can be coldstored but this is expensive and gives rise to moisture condensationwhen exposed to normal workshop conditions making them less suitable formany applications.

Little attention has been given to these materials in the form offoamable powders although they can give significant advantages in termsof low density, low thermal conductivity, gap filling, accurate mouldfilling and lower costs, and some or all of these properties can be usedto advantage in the end applications listed above.

Epoxy resin powders should find even more widespread use if they couldbe produced with a broader range of application and cured physicalproperties.

Desirable properties in such powders include a long usable life atnormal workshop temperatures, a range of curing temperatures from 80° to260° C. preferably from 90° C. to 220° C. within practical cure times, awide band of melt viscosities and a variety of cured mechanical andthermal properties to suit particular uses. These desirable propertiesapply just the same for foamable powders which will normally be used bymelting on contact with a heated surface or applied by techniques suchas electrostatic spraying or placing in a mould or cavity and thenmelted and cured on heating.

The following list expands and helps to describe the properties whichcan be required from such epoxy powders.

(a) Powder Flow

The powder should flow and pour freely with no tendency to sinter oragglomerate over the whole period of its usable life at normal workshoptemperatures. To achieve this property the powder should have a meltingpoint of at least 55° C. and preferably 65° C. as determined by theKofler Heat Bank method.

(b) Shelf Life

This should be at least three months at workshop temperatures andpreferably in excess of 6 months. During this period the melting pointshould not increase to the point where the application properties or thecured product performance shows significant change.

(c) Homogeneity

It is very important that little or no separation of active ingredientsoccurs during storage or application as this can give rise to seriousvariation of properties in the final cured product.

(d) Application Melt Viscosity

Low melt viscosities are very valuable in obtaining smooth well adheredfilms when the powders are essentially used for coating purposes,whereas much higher viscosities may be needed for pressurisedapplications such as moulding powders or composite laminate manufacture.

(e) Curing Temperatures

There are a number of applications where temperatures as low as 100° C.or even lower, are desirable for curing, especially when in contact withheat sensitive materials such as some plastics, or when differentialexpansion stresses should be small. There are also many coatingapplications where very rapid flow and cure is needed to obtain speed ofproduction and in these cases cure temperatures in the range of 180° C.to 260° C. are more useful.

(f) Curing Speed

All curing times must be economically short but a realistic range fallsbetween 4 hours for powders capable of cure at the lowest end of therange, e.g. 80° C. and a few seconds for those designed for rapidproduction lines at 180° C. to 260° C.

(g) Temperature Resistance

Requirements will depend on the actual application and the otherproperties needed but powders capable of giving a glass transitiontemperature Tg, as high as 180° C. or more as measured by DifferentialScanning Calorimetry are valuable in many areas.

(h) Other Properties

Many requirements need to be met to satisfy all applications, butimportant among those are toughness, flame and smoke suppression,chemical resistance and adhesion.

Hitherto, various methods have been proposed for the manufacture ofepoxy powders and they fall principally within the following generalisedtechniques. However, none of these are capable of providing a range ofpowders which can meet the full spread of properties listed under (a) to(h) above.

(1) Hot Melt Mixing

This process is one of blending solid epoxy resins, hardeners and otheradditives as required above the melting point of the resins, thencooling, grinding and sieving to obtain the required particle sizerange. This is an effective and widely used technique but because theresin Kofler Heat Bank melting point should preferably be not less than65° C. it is necessary for the mixing to be carried out in excess of100° C. This method largely excludes hardeners that can be used forlower temperature curing. It also gives difficulties where very highmelt viscosity systems are required due to the need to achievesufficiently low viscosity for mixing.

(2) Blending of Powders

It has been proposed that solid powdered resins, solid powderedhardeners and other additives can be simply mixed together to giveuseful curable powders. GB Patents 1,147,370; 1,164,049; 1,361,909;1,362,455; 1,371,967; 1,379,928; 1,446,870; 1,568,914. U.S. Pat. Nos.4,113,684; 4,120,913. Even if carried out over long periods of time andin very fine particle size this normally leads to blends liable toserious separation on storage or application due to differences inparticle size, shape or density.

To improve the homogeneity and reduce the separation potential of theseblends it has been proposed that they are warm sintered and thenreground and sieved. This is time consuming and expensive and may causeunwanted reaction to occur particularly as this technique is usuallyproposed for highly reactive systems.

Sintering and regrinding cannot totally prevent resin and hardenerseparation as it will always result in a heterogeneous compositionunless the particles are extremely fine so approaching intimate mixingwhen potential unwanted reaction problems become even more likely. Ifthe system is not of high reactivity then the Hot Melt Mixing method ismore satisfactory.

The resins and hardeners used in Powder Blending may be themselves thesolid reaction products of excess resin or hardener with correspondinghardener or resin.

(3) Production of B-Stage Compounds

The term B-stage is used to denote a stage of reaction between resinsand hardeners which is intermediate between the A-stage, completelyunreacted, and the C-stage gelled or cured, where all the reactableingredients have reacted to the point where the mixture has become solidenough to significantly slow further reaction.

In this approach blends are made of resins and hardeners which all reacttogether under the chosen conditions until the reaction products havethe desired melting point, as exemplified by GB Patent 871,350;1,019,925; 1,403,922; 1,529,588. U.S. Pat. No. 4,120,913. The reactiontemperature may be room temperature or above. At this point most of themolecules present have partially reacted to form a mixture of variousoligomers. At this extent of reaction further reaction becomes very slowat room temperature and may be slow enough to allow the product to bepowdered and have some useful shelf life. As the powder is heated in itsfinal application, so the reaction starts again, and as the hardenersare effectively bound into the high molecular weight reaction productsthe melt viscosity is always high and there is rarely sufficient timefor such products to flow readily and usefully in the absence ofexternal pressure before they reach the gelation point and stop flowingat all.

This approach has been studied extensively and often used in theproduction of moulding compounds. However, typical hardeners used inthis way such as 4,4'-diaminodiphenyl methane. 1,3 diamino benzene andvarious tolylene diamines usually only give shelf lives of a few days toweeks at normal shop floor temperatures before gelation.

(4) Differential Reactivity Products

It has been suggested that useful powders can be made by employing twotypes of hardener for liquid epoxy resins (Japanese Patent 51037152) inwhich one hardener type is capable of curing efficiently at least 20° C.below the second hardener type. In the case of the lower temperaturecuring hardener type it is polyfunctional and it is proposed that 40% to70% of the quantity normally used to fully cure the resin be used withthe remaining unreacted epoxy groups being available for cure after flowby the second higher temperature curing hardener type. The disadvantageof this approach is that the use of such a high percentage of the lowertemperature curing polyfunctional hardener which is necessary to obtainnon-sintering powders is close to or above the amount capable of givinggelation and results in the solid composition gelling very rapidly onheating and hence of little value as a normal epoxy powder for coatingsand does not form part of this invention. In the latter case thedisadvantages are very much the same as in the case of B-stagedmaterials as exemplified by very high viscosities and very short flowtimes.

These methods, for similar reasons, also restrict the range and type ofacceptable foamable epoxy powders designed to cure in the range of 80°to 180° C. especially when they contain ingredients which are verysensitive to temperature and this make the Hot Melt techniqueparticularly unsuitable.

Similar problems are encountered in the case of Powder Blending when thefoaming agents are melt incorporated into the resin, the hardener, orboth simultaneously. Where the foaming agents are simply blended intothe system the resulting product is likely to suffer frominconsistencies due to separation on shipment, storage and shop flooruse.

B-staging generally gives little time for good foaming to occur beforerapid gelation.

Until now there has been no general method of producing heat curableepoxy functional powders with sufficient tolerance and flexibility toachieve the full range of desirable physical properties to satisfy theextremes of the application and cured product requirements. So it hasbeen very important to find a method to make such powders which have awide range of properties, excellent stability and can be manufacturedreliably.

We have now discovered a surprisingly simple type of composition whichpermits the safe manufacture of heat curable, powderable, solid epoxyresin systems under extremely mild processing conditions and also allowsall the physical requirements listed under (a), (b) and (c) above to besatisfied as well as the application and property extremes under (d),(e), (f), (g) and (h). This consists of making an epoxy formulationwhich is liquid at 120° C. or below, more usually at normal shop floortemperatures, and adding to it a chemical solidifying system whichreacts very slowly at these temperatures with the epoxy materialspresent.

Accordingly, the present invention provides a one component heat curableepoxy functional powderable materials comprising:

(A) epoxy resin s or epoxy containing compounds,

(B) a solidifying amine system which will react with (A) to give aproduct with a Kofler Heat Bank melting point of between 55° and 120°C., but which is not present in sufficient quantities to allow or causechemical gelation under the reaction conditions chosen for (A) and (B)and which essentially stops solidifying before or when all its activeepoxy additive hydrogen groups are consumed by the epoxy groups,

(C) a hardener system for (A) and the reaction product of (A) and (B)which is different from (B) and which remains substantially unreactedunder the conditions of reaction chosen for (A) and (B) with (A) and(B), and optionally,

(D) an expanding agent which is of low reactivity under the condition ofreaction chosen for (A) and (B) and which is of low reactivity at normalworkshop temperatures in the final solid epoxy formulation andoptionally,

(E) Other additives that may be required to modify the physicalproperties of the cured or uncured composition.

The solidifying system must be picked to give very little reactionduring the time it is in mixing with the epoxy resin and hardeners, bywhatever method this is done, so that there is very little viscosityrise or temperature rise during the blending operation and hence makingthe filling of large or small simple or complicated containers arelatively easy task. Alternatively mixing may take place in the finalcontainer if required.

The solidifying reaction must be a simple amine addition reaction withthe epoxy groups and must stop when the addition reaction stops. Notertiary amines may be present in the initial mixture or generatedduring the reaction which could significantly react under the conditionschosen for the solidification reaction. Such reactions severlycompromise safety during bulk mixing, solidification once mixed and thesoftening point stability and shelf life of the resultant product. Thesolidifying system must be picked to satisfy these criteria.

This general composition also allows, either complete homogeneity of allthe reactive ingredients or effective encapsulation of those not solublein the original blend and also allows a wide range of viscosities andgel times to be designed into the product.

The solidifiable epoxy resin composition is made by blending (A), (B),(C), (D) and (E) together by any convenient batch or continuousoperation but in such a way that at least (A) and (B) becomehomogeneous. The reaction between (A) and (B) may be carried out at anysuitable temperature and condition provided that neither it, nor theenothermic heat generated from it causes (C) or (D) to substantiallyreact whilst it is taking place.

By adopting the technique of this invention it becomes a relativelysimple matter to produce optionally foamable powderable solid epoxyresin compositions which avoid the problems or difficulties or extremeconditions used with most current and other proposed methods for makingpowderable solid epoxy resin formulations.

It now becomes possible to avoid:

(i) The Hot Melt Mixing of solid epoxy resins with hardeners and otheringredients at relatively high temperatures. This invention allows theuse of liquid resins or low temperature melting resins or blends.

(ii) The Blending of Powders together and the consequent chances ofphysical separation inhomogeneity and variable physical properties. Thisinvention overcomes these disadvantages as it allows for liquid orsoluble hardeners which will normally result in homogeneous compounds oralternatively for solid hardeners which can be finely ground andthoroughly dispersed in the resin or other components before finalmixing, so that the resultant powder is effectively homogeneous and thefine hardener particles basically encapsulated in the solid resin.

(iii) The Production of B-stage Compounds of all types with theirassociated problems of high viscosity for processing and frequently veryshort shelf life. This invention specially sets out to avoid B-stagingby creating the solid resin "in-situ" under mild conditions thus leavingthe ultimate hardener effectively unreacted. This permits much greatercase of wetting and flow of the molten powder before gelation whenrequired.

It now becomes possible to obtain:

Powders with either low or high melt viscosities as required through thecareful selection of (A) and (B).

Powders curing in 2 hours at 100° C. or less or a few seconds at 180° C.to 260° C. by the careful selection of (C).

A wide range of desired mechanical and thermal properties by the carefulselection of (A), (B) and (C).

Ready modification of physical and mechanical properties may also beachieved by the introduction of additives. (E) including those heatsensitive in nature.

All of the above advantages and desired properties complemented by thelong workshop temperature shelf life desirable for simple storagetransportation and use.

The epoxy resins or epoxy group containing compounds (A) employed inthis invention may be glycidyl ethers, glycidyl amines, glycidyl estersor cycloaliphatic compound or combinations of these includinghalogenated versions where required. Preferred epoxy resins and blendsare those which are suitable liquids for ready mixing with the otheringredients at suitable temperatures which will usually be below 120° C.Epoxy resins or epoxy containing compounds or blends of them which areliquid at room temperatures are the most convenient.

The preferred solidifying systems (B) used to convert the liquid resinsare principally compounds or mixtures of compounds whose most reactivegroups relative to the epoxy materials employed are primary or secondaryamines. Epoxy reactive tertiary amines under the conditions of reactionchosen for (A) and (B) are not acceptable for this invention.

Of particular usefulness in this process are aromatic and cycloaliphaticprimary and secondary amines and blends of these. The major advantage ofthese amines, particularly the aromatic amines, is the low rate ofreactivity coupled with the extremely long life at normal ambienttemperatures of their reaction products with the resins. With themajority of compounds from these classes of amines the life of thereaction product with the resins greatly exceeds that of the life of theresins with their primary hardeners (C). Some alicyclic, heterocyclicand aliphatic amines are also effective as advancing agents and thosewhich comply with cessation of reaction once their amino hydrogen atomshave been consumed by the epoxy resins and considered as part of thisinvention. In all cases it is essential that the tertiary aminesgenerated during the solidification reaction have very low reactivitywith epoxy groups under the conditions of reaction chosen for (A) and(B) and afterwards during storage. The solidifying amines are usuallyand mostly difunctional and/or polyfunctional with respect to the epoxycompounds (A) although monofunctional amines can be used to some extentif of value to a particular composition.

Difunctional maines may be used at any desired ratio with difunctionalepoxy resins but greater than difunctional amines only to levels wheregelation does not occur. The solidifying systems may contain a varietyof other groups but these should only be of very low or no reactivitytowards the epoxy groups involved under the reaction of (A) and (B).

Most useful are those solidifying systems which react gradually tosubstantial completion at room temperatures over a period of around 2-14days. These permit the safe manufacture of batches in excess of 100litres in a realistic mixing time with little temperature rise in themixing vessel or during discharge and smooth reaction to the requiredphysical state in most practical containers, however mixed over apractical timescale. Under these conditions the heat of reactiongenerated by the solidification process is evenly dissipated byconduction and radiation and results in no more than acceptabletemperature rises at any stage in the process.

The primary controlling factor being that the mixture reactiontemperature rise whether in the mixing vessel or the containers shall bebelow that required to cause significant reaction between (A), (C) or(D).

Should it be desirable to speed the solidification in the finalcontainer this can be achieved by heating provided the temperature useddoes not cause significant reaction of (C) with (A) or the reactionproduct of (A) and (B) either by direct heat or that evolved bycompleting the reaction between (A) and (B) or by the addition ofaccelerators such as carboxylic acids which do not adversely affect thesoftening point stability.

The solidifying systems must be present in such quantities that whentheir amino hydrogen atoms are all substantially reacted with the epoxymaterials (A) under the conditions set for reaction (A) and (B) theproduct is not chemically gelled and has a melting point which isgreater than 55° C. and lower than 120° C. and is essentially stable forgreater than 6 months at 22° C. The resultant product is a brittle solidat 22° C. which could be cast into various physical forms such as sticksor pellets, but is essentially useful for grinding into powders.

The selection and quantity of the solidifying agent will also influencea variety of properties such as melt viscosity, strength, toughness andheat resistance and by careful choice advantages may be designed intothe uncured or cured products resulting from the use of the process.

The hardener systems, (C) for the epoxy compounds (A) and the reactionproducts between (A) and (B) can be selected from the wide variety ofthose well known in the field of epoxy chemistry other than acidanhydrides which react preferentially with the advancing agents (B).Typical but not exclusive examples of useful hardeners are aromaticamines such as diaminodiphenyl sulphones, boron trifluoride aminecomplexes, latent imidazoles, carboxylic acids, biguanides, hydrazides,dicyandiamide, latent epoxy amine adducts and substituted ureas. Asexplained a main requirement of the hardener is that it should notsubstantially react whilst (A) and (B) are being reacted to form theepoxy composition which has a melting point greater than 55° C. Theremay be one or several hardeners used together, some of which mayaccelerate the curing rates of the other provided they comply with therequirement immediately above.

The expanding agents (D) may be of any type which does not adverselyinterfere with the production of the solid epoxy composition nor itsability to cure satisfactorily. The expansion obtained may result fromchemical or physical reactions or both. An important feature is that thefoaming agent should not cause substantial foaming during the processfor the production of the solid epoxy compositions, nor on storage of itin any form at normal workshop temperatures or below. All significantexpansion should take place during the actual curing cycles.

Examples of suitable expanding agents include

Azodicarbonamide, Azodiisobutyronitrile, Benzene sulphonhydrazide,Dinitroso pentamethylene tetramine, Oxybis benzene sulphonhydrazide, ptoluene sulphonyl hydrazide and Expandable plastic such as those soldunder the Trade Name Expancel.

These are largely spherical shells of varying composition such aspolyvinylidene chloride and or polyacrylonitrile plus othercopolymerised additives, and the inside contains isopentane±air.

Other additives, (E) which can be used to modify the physical propertiesof the cured or uncured compositions include but are not limited tothixotropes, toughening agents, wetting agents, surfactants, fibrousmaterials, dyes, pigments, fillers, flame retardants, smokesuppressants, coupling agents, hollow microspheres, flow assistingmaterials, fusible glasses and stabilisers.

The following Examples demonstrate some of the wide range ofcompositions which may be successfully used according to this invention.

EXAMPLE 1

A liquid Bisphenol A epoxy resin (EPIKOTE 828 - SHELL CHEMICAL CO.) withan epoxy content of approximately 5.3 gram equivalents of epoxy oxygenper kilogram was blended with amino benzene and dicyandiamide asfollows:

    ______________________________________                                        EPIKOTE 828         100 parts by weight                                         amino cyclohexane  18 parts by weight                                         dicyandiamide  4 parts by weight                                            ______________________________________                                    

This mixture was thoroughly dispersed at 22° C. After five days themixture was brittle and easily powdered and had a Kofler Heat Bankmelting point of 65° C. 3 years later this melting point was 68° C. Aportion was heated for two hours at 80° C. and on cooling the blendcould easily be powdered and had a Kofler Heat Bank melting point ofapproximately 72° C. and remained unsintered for a least 3 years whenstored at 22° C. On heating to 180° C. the powder melted to a freeflowing liquid, then gelled and after 60 minutes was a strong, tough,thermoset, plastic compounds.

EXAMPLE 2

A crystalline Bisphenol F resin (PY 306 - Ciba-Geigy) with an epoxycontent of approximately 6.2 gram equivalent of epoxy oxygen perkilogram was blended well with 4 aminotoluene and 4,4' diaminodiphenylsulphone as follows:

    ______________________________________                                        PY 306               100 parts by weight                                        4aminotoluene  26 parts by weight                                             44' diaminodiphenyl sulphone  10 parts by weight                            ______________________________________                                    

The 44' diaminodiphenyl sulphone was sieved through a B.S. 300 meshsieve to obtain a fine powder free from lumps and this was dispersedthoroughly in 50 parts of liquid PY 306 at 22° C. obtained by warmingthe crystalline resin to 100° C. and allowing it to cool. The4aminotoluene was warmed with the remaining 50 parts of liquid PY 306 at55° C. until it melted and dissolved.

The two parts were then mixed together and allowed to stand at 22° C.for two days. They were then heated to 60° C. for five hours. Theresulting solid was easily powdered and had a Kofler Heat Bank meltingpoint of around 65° C. When cured for two hours at 180° C. it was atough solid with a glass transition point of around 120° C. After sixmonths at 22° C. the melting point had increased by only 5° C. and thepowder was free flowing.

EXAMPLE 3

The following mixture was prepared:

    ______________________________________                                        EPIKOTE 828            90.0 parts by weight                                     butane diol diglycidyl ether 10.0 parts by weight                             4,4' diamino 3,3' dimethyl dicyclohexylmethane  8.5 parts by weight                                 aminobenzene  9.6 parts by weight                       dicyandiamide  4.0 parts by weight                                          ______________________________________                                    

The finely powdered dicyandiamide was thoroughly mixed into the lowviscosity blend of the other ingredients and the dispersion was placedinside a polythene bag. After 4 days at 22° C. it was a brittle solid.The solid was then heated for 3 hours at 70° C. It was powdered and hada Kofler Heat Bank melting point of around 65° C. Three months later itstill poured readily. On heating for 1 hour at 180° C. the mixture firstmelted, then flowed readily, gelled and became a tough solid.

A further mixture of this composition was prepared and left for 7 daysat 22° C. After this time it was a brittle solid with a Kofler Heat Bankmelting point of 61° C. Six months later it poured readily and themelting point had increased by 4° C.

EXAMPLE 4

The following mixture was prepared:

    ______________________________________                                        DER 332                100.0 parts by weight                                    4,4' diamino 3,3' dimethyl dicyclohexyl methane  5.8 parts by weight                                aminobenzene  9.3 parts by weight                       4,4' diaminodiphenyl sulphone  16.4 parts by weight                         ______________________________________                                    

DER 332 is a nearly pure Bisphenol A diglycidyl ether solid by DOWChemical Co. The DER 332 was warmed to 50° C. to melt it and aftercooling was mixed with the 4,4' diaminodiphenyl sulphone powder. Thisblend was run through a triple roll mill to obtain a good dispersion.The remaining amines were added and the resultant blend was covered witha polythene film and allowed to solidify at 22° C. for 4 days. Themixture was then heated for two hours at 60° C. and cooled. It was abrittle solid with a Kofler Heat Bank melting point of around 70° C. Itwas powdered and six months later had increased in melting point byapproximately 2° C.

The powder was heated in a released container for 2 hours at 100° C. 4hours at 150° C. and then post cured for 4 hours at 200° C. Theresultant polymer possessed a TG of 182° C. as measured by the D.S.C.method.

EXAMPLE 5

The following mixture was prepared:

    ______________________________________                                        DEN 438            20 parts by weight                                           DER 331 80 parts by weight                                                    aminobenzene 20 parts by weight                                               Anchor 1040  3 parts by weight                                              ______________________________________                                    

DEN 438 is a semi solid epoxy novolak resin sold by DOW Chemical Co withan epoxy content of about 5.6 gram equivalents of epoxy oxygen perkilogram.

DER 331 is a liquid Bisphenol A epoxy resin sold by DOW Chemical Co withan epoxy content of about 5.2 gram equivalents of epoxy oxygen perkilogram.

Anchor 1040 is a coordination complex of boron trifluoride marketed byANCHOR Chemical Co.

The two resins were warmed and mixed together and allowed to cool to 22°C. The remaining ingredients were added with stirring to give anhomogeneous blend. After three days the mixture was heated at 55° C. Oncooling it was a brittle solid which was easily powdered. It had aKofler Heat Bank melting point of around 65° C. On heating to 180° C.for 60 minutes it melted, gelled and cured to give a hard thermosetplastic.

After six months the powder flowed readily and melted at around 70° C.

EXAMPLE 6

The following mixture was prepared:

    ______________________________________                                        EPIKOTE 828          100.0 parts by weight                                      4,4' diamino diphenyl methane  8.8 parts by weight                            aminobenzene  6.1 parts by weight                                             dicyandiamide  3.5 parts by weight                                            3(4 chorophenyl) 1.1 dimethyl urea  2.7 parts by weight                       fumed silica  3.5 parts by weight                                             carbon black  1.0 parts by weight                                           ______________________________________                                    

The carbon black, dicyandiamide and substituted urea were mixed with 50parts of the liquid resin and triple roll milled to obtain a gooddispersion. This was then blended with a solution of the 4,4' diaminodiphenyl methane in the remaining resin and the other ingredients. Thewhole mixture was placed in a container and after 7 days at 22° C. theblend was a brittle solid. It was heated for 2 hours at 60° C. thencooled and powdered. It had a melting point of around 60° C. This powderremained free flowing for at least 6 months at 22° C. and showed noincrease in melting point. The powder was applied to clean steel rods,heated to 180° C. by fluidised bed techniques and gave a smooth blackcoating which adhered well and was very tough after a cure of 180minutes at 100° C.

EXAMPLE 7

The misture in Example 1 was poured into a tray and heated for 5 hoursat 80° C. On cooling it was a brittle, powderable solid with a meltingpoint of 80° C. After 9 months at 22° C. this powder flowed freely andretained the same melting point. On heating to 180° C. for 1 hour itcured to form a tough, thermoset product.

EXAMPLE 8

A liquid Bisphenol A epoxy resin (EPIKOTE 828 - SHELL CHEMICAL CO.) withan epoxy content of approximately 5.3 gram equivalents of epoxy oxygenper kilogram was blended with aminobenzene. 44' diamino diphenylsulphone, 44' oxybis benzene sulphonylhydrazide and a fumed silica.

All the powders were passed through a B.S. 300 mesh sieve to remove anyagglomerates and were then thoroughly dispersed by passing a triple rollmill with 50 parts of the liquid resin.

The composition employed was:

    ______________________________________                                        EPIKOTE 828           100.0 parts by weight                                     aminobenzene  19.7 parts by weight                                            44' diamino diphenyl sulphone  6.6 parts by weight                            44' oxybis benzene sulphonylhydrazide  1.0 parts by weight                    fumed silica  2.0 parts by weight                                           ______________________________________                                    

All the components were mixed together and placed in a released tray.After five days the solid blend was heated for two hours at 60° C. Oncooling to 22° C. the blend could easily be powdered. The powder had aKofler Heat Bank melting point of approximately 70° C. After storing atambient temperature for six months the softening point was approximately73° C. and no sintering had occured. On heating to 180° C. the powdermelted, rapidly increased in viscosity, foamed and cured. After 60minutes a strong tough, thermoset foam was obtained.

EXAMPLE 9

The following mixture was produced:

    ______________________________________                                        EPIKOTE 828           100.0 parts by weight                                     44' diamino 33' dimethyl dicyclohexyl methane  10.6 parts by weight                                benzylamine  7.1 parts by weight                         azodiisobutyronitrile  3.0 parts by weight                                    dicyandiamide  3.5 parts by weight                                            3(4chlorophenyl) 1,1 dimethylurea  2.9 parts by weight                        fumed silica  8.0 parts by weight                                           ______________________________________                                    

All the solids with the exception of the fumed silica were sieved andmilled with 10 parts of liquid resin as per EXAMPLE 8. The fumed silicawas added as the last ingredient to the mixture, which then became verythixotropic. The mixture was placed in a tray and was covered with apolythene film. After five days the mixture was a brittle solid. Onpowdering the Kofler Heat Bank melting temperature was 65° C. Whentested after storage at normal ambient temperature for 850 days thesoftening temperature had increased by 13° C. to 80° C. and the powderflowed freely with no sign of sintering.

After initial powdering the coarser and finer particle fractions wereremoved leaving a particle size range between 250 and 2500 microns. Thepowder was placed into a tube of 0.65 centimetre diameter, closed at oneend to the point where the tube was full of powder. The filled tube wasthen put into an oven and heated for 1 hour at 120° C. At the end ofthis time the tube was filled with a strong cured foam which was stillof approximately the same volume as the tube. On careful examination ofthe physical curing process it became clear that the compositionparticles melted but did not flow and then expanded to fill the voidsbetween them to give the final foam filled tube. The density of thisfoam was 0.6 grams per cubic centimetre. It will be apparent to workersin this field that the powder of this example could be used as a lowerdensity gap filling adhesive if the tube was clean and receptive tobonding or as a low density moulding or casting material if the tube wasrelease treated to prevent adhesion.

EXAMPLE 10

The following mixture was produced:

    ______________________________________                                        EPIKOTE 828           100.0 parts by weight                                     44' diamino 33' dimethyl dicyclohexyl methane  10.0 parts by weight                                aminocyclohexane  6.6 parts by weight                    phenolic microbaloons  10.0 parts by weight                                   Expancel 550 DU  3.0 parts by weight                                          dicyandiamide  3.5 parts by weight                                            3(4chlorophenyl) 1,1 dimethylurea  2.9 parts by weight                        fumed silica  2.0 parts by weight                                           ______________________________________                                    

Expancel 550 DU is a type of very small diameter expandable plasticbead. Phenolic microballoons are very low density hollow phenolicspheres. The mixture was thoroughly blended with the Expancel beingadded as the last ingredient and then placed in a tray. It was coveredwith a film of polythene and stored at 25° C. for 4 days. After thisperiod it was powdered and possessed a Kofler Heat Bank melting point ofapproximately 65° C. After 700 days storage at normal ambienttemperature the melting point had increased to 80° C. and no sinteringhad occurred.

A similar experiment with a tube filled with the powder was carried outas an in Example 9. In this case the powder melted and flowed somewhatduring the heating cycle, but then expanded and overfilled the tube whenfully cured after 60 minutes at 120° C. The initial powder had a volumefilling density of 0.4 grams per cubic centimetre and the wellstructured cured foam a density of 0.3 grams per cubic centimetre.

EXAMPLE 11

The following mixture was produced:

    ______________________________________                                        diglycidylether of Bisphenol-F                                                                       50.0 parts by weight                                     diglycidylether of tetrabromobisphenol-A 50.0 parts by weight                 aminobenzene  5.4 parts by weight                                             44' diamino diphenyl methane  7.7 parts by weight                             Anchor 1040  3.0 parts by weight                                              44' oxybis benzene sulphonylhydrazide  1.0 parts by weight                    fumed silica  6.4 parts by weight                                           ______________________________________                                    

Anchor 1040 is a coordination complex of boron trifluoride marketed byANCHOR Chemical Co.

The Bisphenol-F and tetrabromobisphenol-A resins were melted together at100° C., and when mixed, the 44' diamino diphenyl methane was added withrapid stirring until dissolved and the whole blend then quickly cooledto 22° C. The remaining liquids and solids were added with thoroughstirring and the mixture was placed in a released tray. After five daysthe blend was heated to 40° C. for four hours and was then broken andpowdered. It possessed a Kofler Heat Bank softening temperature ofaround 60° C. After six months the softening point increased to 74° C.On heating to 180° C. the powder coalesced and foamed and yielded astrong thermoset product after curing for two hours at 180° C.

EXAMPLE 12

A composition identical to Example 9 was prepared, other then the fumedsilica level was reduced to 4.5 parts per hundred parts of resin byweight. This product was powdered and sieved to a particle size rangebetween 200 and 800 microns.

This product was applied to clean steel rods, heated to 120° C. by thefluidised bed technique. The powder melted and adhered to the rods andafter curing for 30 minutes at 120° C. gave a smooth, strong foamedcoating. A similar experiment carried out with the rods heated to 200°C. gave a coating which was foamed and adhered without any extra curing.

As may be seen from the foregoing examples, this chemical approach tothe production of curable optionally foamable epoxy powders employsconditions much less rigorous than the method of Hot Melt Mixing solidresins with hardeners, which require mix temperatures of around 100° C.or frequently above.

With the current invention, in many cases, the epoxy resin blends areliquid at 22° C. and the solidifying reaction takes place at the sametemperature.

If further heating is required to obtain a stable pourable powder at 22°C. or thereabouts it rarely needs to be above 50°-60° C.

The simplicity and mildness of the approach to making these epoxypowders enables the incorporation of a wider variety of heat sensitiveadditives including hardeners and accelerators than is possible with theHot Melt method and yields powders with outstandingly long shop floortemperature storage times.

The use of temperatures above 60° C. to obtain suitable solids andpowders is only necessary to increase speed or throughput in production.

It will be clear from the examples that most of the compositions ofmatter disclosed here could be cast into specific shapes rather thenground into powder if required, or that the powders could be melted orsintered into specific shapes as well. It will also be clear that thecured products could find use as adhesives, encapsulants, insulatingmaterials and mouldings as well.

What is claimed is:
 1. A reactive resin composition, which is a fusible,solid optionally foamable, heat curable, epoxy functional reactionprouct with a Kofler Heat Bank melting point of not less than 55° C.,formed by mixing together(A) epoxy resins of epoxy group containingcompounds (B) an amine solidifying system present in insufficientquantities to cause gelation after all the amino hydrogen atoms areconsumed by epoxy groups, under the reaction conditions chosen for (A)and (B), and which yields a product with a Kofler Heat Bank meltingpoint of greater than 55° C. and less than 120° C. and melting pointstability of at least six months normal workshop temperatures, (C) ahardener system for (A) and the reaction product of (A) and (B) which isdifferent from (B) and remains substantially unreacted under theconditions of reaction chosen for (A) and (B) with (A) and (B) and whichis of low reactivity at normal workshop temperatures in the final solidepoxy formulation, and optionally, (D) an expanding agent which is oflow reactivity under the conditions of reaction chosen for (A) and (B)and which is of low reactivity at normal workshop temperatures in thefinal solid epoxy formulation, and optionally (E) other additives thatmay be required to modify the physical properties of the cured oruncured composition.
 2. A composition according to claim 1 where themixture is heated to speed the solidification reaction between (A) and(B) without significantly activating hardener (C) or expanding agent(D).
 3. A composition according to claim 1 where the partiallysolidified composition may be heated to speed completion provided thetemperature reached due to the completion of the solidification reactiondoes not significantly activate hardener (C) or expanding agent (D). 4.A composition according to claim 1 which, when ground is a free flowingpowder at normal workshop temperatures.
 5. A composition according toclaim 1 which cures with the range of 80° C. to 260° C.
 6. A compositionaccording to claim 1 where the majority of the epoxy groups are presentas glycidyl ether, glycidyl amine, glycidyl ester, cycloaliphatic andother epoxy resins.
 7. A composition according to claim 1 where theepoxy group containing compounds (A) are free flowing liquids at 120° C.or less.
 8. A composition according to claim 1 where the solidifyingagents are mainly aromatic cycloaliphatic or alicyclic primary amines,secondary amines or mixtures of the two together with any acidaccelerator.
 9. A composition according to claim 8 where the majority ofthe solidifying amine groups are difunctional or difunctional and polydifunctional with respect to the epoxy groups.
 10. A compositionaccording to claim 1 where suitable hardener systems include aromaticamines such as 44' diaminodiphenyl sulphone, boron trifluoride aminecomplexes, latent imidazoles, carboxylic acids, biguanides, hydrazides,dicyandiamide, latent epoxy amine adducts and substituted ureas.
 11. Acomposition according to claim 1 where expanding agents are present andinclude those generating gases by chemical decomposition or by boilingof liquids or expansion of gases contained within expandable shells. 12.Cured products obtained by heating a composition according to claim 1.